1. Field of the Invention
This invention relates to a method of manufacturing an exhaust gas catalyst capable of lowering cold-start emissions.
2. Background Art
The need to lower vehicle exhaust emissions continues to create challenges, especially in the wake of stringent environmental regulations. The need to lower cold-start emissions is at the heart of most emissions reduction strategy, since cold-start emissions account for a significant portion of exhaust emissions from any given vehicle. During startup, hydrocarbons can be passed through the exhaust system before the catalyst can heat up and convert the hydrocarbons to more desirable gases. Although a large portion of hydrocarbons are reduced, an amount of hydrocarbons and other undesirable gases may be allowed to pass through the exhaust system without reduction thereof.
One solution to the cold-start emission problem is providing a material that is able to give off oxygen to the catalyst during startup conditions such that the “light-off” temperature of the catalyst is accelerated. The light-off temperature is the temperature at which the catalyst reacts with hydrocarbons and other exhaust gases to reduce these gases, which are undesirable, to more desirable gases such as carbon dioxide. Oxygen, when fed to the catalyst, creates an exothermic reaction to the catalyst, resulting in increased temperature which allows the catalyst to reach the light-off temperature more quickly.
Currently, palladium is used with a cerium-zirconium mixed oxide support, an aluminum oxide support, or a mixture thereof to give off oxygen at startup conditions (low temperature), in order to accelerate light-off of the catalyst. However, palladium is an extremely expensive material which typically contributes to approximately 95% of the total cost of the catalyst. Recent studies have thus focused on methods and materials to reduce the consumption of palladium while providing an effective means for accelerating the light-off temperature of the catalyst.
The use of additional hardware has also been proposed to solve the cold-start problem. In some cases, the additional hardware allows the exhaust system catalyst to be heated directly in order to accelerate light-off of the catalyst. For example, an electrically heated catalyst may be used where the catalyst is heated directly by an electric heater. Prior to startup, current is run through the heater via the vehicle battery, and the heat produced accelerates light-off of the catalyst and, in turn, lowers the cold-start emissions.
Another example of an active approach is to allow fuel to combust near the catalyst to quickly raise the temperature thereof. This is accomplished by running lines and having an ignition system disposed on the vehicle. Generally, systems that incorporate additional hardware, such as the examples mentioned above, result in high costs for implementation.
Thus, what is needed is a cost effective solution to the cold-start emissions problem.